1. Field of the Invention
The invention relates to a slip mechanism for anchoring an inner tubular conduit to the inner bore of a surrounding outer tubular conduit, for example, anchoring of a production string to a well casing.
2. Description of the Prior Art
There is a need for devices, commonly called slip mechanisms, for achieving the anchoring of a small diameter tubular member to the bore wall of a surrounding larger diameter tubular member, generally the well casing. Such devices are employed, for example, in packers, hangers and bridge plugs. The commonly utilized forms of slip mechanism involve axially spaced upper and lower cone or cam elements which are respectively mounted for relative axial sliding movement between the two tubular members to be anchored. Each cam or cone element is provided with a plurality of peripherally spaced, axially extending slots and each slot slidably accommodates a slip member which is of generally rectangular configuration and has wall bore engaging teeth formed on its outer side. The bottom portion of one end of each slip member is shaped to form a cam surface which co-operates with a correspondingly shaped bottom surface of the respective axial slot to urge the slip outwardly. All of the teeth of the slip members mounted in the lower cone element may be downwardly inclined to engage the bore wall of the outer tubular member and prevent downward movement of the slips and associated cone, while the engaging teeth of the set of slip elements mounted in the other cone element may be inclined in the opposite direction and act to engage the outer bore surface and prevent upward movement.
When such slip elements are employed in a packer, the two cam elements and abutment blocks are normally separated by annular bands of elastomeric material. Thus, axial movement of the two cone elements toward each other effect the concurrent expansion of the slip elements into engagement with the bore wall of the outer tubular member and at the same time effect the compression of the elastomeric elements between the annular abutment blocks to cause a radial expansion of such elements into sealing engagement with the same bore wall. The compressive forces required to effect such radial expansion of the slip elements and elastomeric seal elements may be generated either by mechanical or hydraulic actuation by elements disposed respectively above and below the upper and lower cone elements. While not strictly necessary, it is desirable that each of the slip elements have an annular segment cross section, and this necessarily results in a complex structure to produce by conventional machining operations.
Additionally, due to the fact that each set of slip elements is separately actuated by relative axial movements of its respective supporting cone and abutment block members, it generally happens that one set of slip elements engage the bore of the outer wall prior to the other set, thus, additional axial movement of the actuating member for the other set of slip mechanisms must be provided in order to insure the rigid engagement of its cutting teeth with such bore surface. The greater the extent of axial movement required to effect the setting of both sets of slip mechanisms, the more complex and expensive will be the actuating mechanism for the slip mechanisms.